1. Field of the Invention
The present invention relates to an adhesive composition which is particularly suited for using at a step of die-bonding a semiconductor device (semiconductor chip) on an organic substrate or a lead frame and a step of dicing a silicon wafer and the like and die-bonding a semiconductor chip on an organic substrate or a lead frame, an adhesive sheet having an adhesive layer comprising the above adhesive composition and a production process for a semiconductor device using the above adhesive sheet.
2. Description of the Related Art
A semiconductor wafer of silicon, gallium arsenide or the like is cut and separated (dicing) into small pieces (IC chips) of devices and then transferred to a bonding step which is a subsequent step. In this case, the semiconductor wafer is subjected to the respective steps of dicing, washing, drying, expanding and picking-up in the state that it is adhered in advance on an adhesive sheet, and then it is transferred to a bonding step which is a subsequent step. Furthermore, for such purposes as protecting a semiconductor chip from the surrounding environment and making it into a shape easily mountable on a print board, a semiconductor package is produced, in some cases, by sealing a substrate on which an IC chip is bonded with a mold resin after the bonding step.
In order to simplify the picking-up step and the bonding step among the above steps, for example, adhesive sheets for dicing and die-bonding which are described in patent documents 1 to 4 and which are provided with both a wafer-fixing function and a die-adhering function are proposed.
Adhesive sheets comprising an adhesive layer comprising a specific composition and a base material are disclosed in the patent documents 1 to 4. The above adhesive layer has a function of fixing a wafer in dicing the wafer, and irradiation thereof with an energy beam reduces an adhesive strength thereof and makes it possible to control the adhesive strength between the adhesive layer and the base material, so that when picking up the chip after finishing dicing, the adhesive layer is peeled off together with the chip. When the IC chip provided with the adhesive layer is mounted on a substrate and heated, an adhesive strength of a thermosetting resin contained in the adhesive layer is revealed to complete adhesion between the IC chip and the substrate.
The adhesive sheets disclosed in the patent documents described above enables so-called direct die-bonding and makes it possible to omit a step of coating an adhesive for adhering a die.
On the other hand, very severe physical properties are required to semiconductor devices in recent years. For example, package reliability under severe hot and humid environment is required in an examination of a term of quality assurance. However, a reduction in a thickness of a semiconductor chip itself results in a reduction in a strength of the chip, and the package reliability under severe hot and humid environment has not necessarily been satisfactory.
In a surface mounting carried out in connection of electronic parts in recent years, a surface mounting method in which the whole part of a package is exposed to high temperature of not lower than a melting point of a solder is carried out(reflow process). In recent years, a mounting temperature is elevated from 240° C. which has so far been carried out to 26° C. due to transfer to a solder containing no lead from the viewpoint of attentions to the environment to increase a stress produced in the inside of a semiconductor package, and the risk of producing peeling of adhesive interface between a semiconductor chip and an adhesive sheet and package crack is further elevated.
In other words, an adhesive sheet is required whose quality such as an adhesive strength does not deteriorate even exposed to severe hot and humid environment and which does not cause package crack and the like even exposed to a high temperature condition of 260° C. after that, that is, can achieve high package reliability, as well as enables the so-called direct die-bonding as aforementioned.
As a technology to meet the tough requirements for physical properties, especially requirements for resistance to hot and humid environment, for example, Patent Document 3 discloses an adhesive tape having an adhesive layer formed from an energy beam-curable adhesive component, an epoxy resin and a phenol resin.
In Patent Document 3, the energy beam-curable adhesive component mentioned above is exemplified by a (meth)acrylate copolymer comprising such a constitutional unit derived from a (meth)acrylate monomer and the like and there is described that the epoxy resin acquires a property of firmly adhering an adherend upon heating and that the phenol resin reacts with the epoxy resin upon heating to form a cured product.
Furthermore, Example 5 of Patent Document 5 discloses an adhesive composition containing an acrylic copolymer, an epoxy resin and a heat-activatable latent epoxy resin curing agent (phenol resin). On the other hand, Patent Documents 2, 4, 5 and the like disclose a benzyl(meth)acrylate as an example of a (meth)acrylate monomer used for constituting an adhesive component.
However, there are no specific descriptions about the amount of benzyl(meth)acrylate to be used and the like in these documents.
Patent document 1: JP-A-1990-32181
Patent document 2: JP-A-1996-239636
Patent document 3: JP-A-1998-8001
Patent document 4: JP-A-2000-17246
Patent document 5: JP-A-2006-335860